1. Field of the Invention
The present invention relates to a dendritic compound, and more particularly, to a dendritic compound suitable for chelating with metal cations.
2. Description of Related Art
Nuclear Magnetic Resonance Imaging (MRI) is one of the most significant diagnosing techniques in modern medical science. Compared to X-rays or CT scanning, MRI provides multi-angle scanning which can be applied to the central nerve system, the skeletal nerve system, the abdomen, the chest, angiography, cholangiography, and the most important and valuable of all, to discover and diagnose tumor tissues.
The principle of MRI is to transform the hydrogen atoms within human tissues into tiny radio transmitters. Under the same magnetic field change, hydrogen atoms within water or other molecules transmit different signals. MRI traces these signals and forms the 3-D image of a human body through Fourier Transfer. In other words, the greater the differences in each radio-transmitted signal, the clearer contrast will be transformed. So far, it is known that the use of super-paramagnetic elements, such as Gadolinium (Gd), can enhance the contrast. As a result, the density of super-paramagnetic elements is the critical factor for the clarity of image.
In addition, due to the fact that free Gd is toxic, a chelator must be added when the Gd is applied to human bodies. The addition of the chelator can decrease the chemical reaction during body circulation. Diethylenetriamine pentaacetic acid (DTPA) is one of the most common and commercially mass produced chelators for application in MRI.
However, when applying the commercialized non-polymer carrier Gd-DTPA as an imaging agent, chelators with small molecule weight penetrate vascular endothelial cells easily and thus extensive losses occur while circulating. Furthermore, it requires high concentration of Gd to achieve the desirable image. In addition to the potential danger of toxicity caused by high concentration of Gd, it is also difficult to massively accumulate an imaging agent on a certain position. Therefore, there exists a great disadvantage for clinical application of prior art non-polymer Gd-DTPA imaging agents.